The manipulation of spin currents is crucial in spintronic research and has been a topic of great interest
due to its potential application in new spin-based technologies [1]}, [2]}. By definition, spin current involves
an effective transport of angular momentum and, opposite to the conventional (electrical) charge current, the spin current can also
be achieved in insulating materials. A spin current is obtained in conductors when up- and down-oriented electron
spin fluxes show different densities, as occurs in the Spin Hall Effect [3]} or using spin valves for filtering
one of the spin-oriented conduction electrons, for example. On the other hand, in magnetic insulators, the spin transport is provided by
magnons (the quanta of spin-wave) [2]}, [5]} or even spinons (neutral half-integer spin
excitation) [6]}, [7]}, [8]}. Since the current in insulators does not involve charge transport,
it is defined as a pure spin current.
